Wireless control has recently become a ubiquitous trend in the field of communication, especially for building management systems. Wireless technologies present major advantages in terms of freedom of placement, portability, and installation cost reduction, since there is no need for drawing cables and drilling. Thus, such technologies are particularly attractive for interconnecting detection, automation, control or monitoring systems using sensor devices such as light switches, light dimmers, wireless remote controllers, movement or light detectors, that have to be set up far away from each other and from the devices they control, e.g. lights.
One of the drawbacks appearing in networks of the like relates to device powering. Indeed, since the devices are not wired, they cannot receive power necessary for performing all the operations required in the network from the mains or via the connection with the controller. Thus, it has been envisaged to equip such devices with built-in batteries. However, since the devices are quite size-constrained, batteries may not be of a large size, which results either in a reduced device lifetime, or in a labour intensive battery replacement. Moreover, used batteries result in toxic waste.
It has been suggested to remedy this issue by equipping sensor devices with self-sustained energy sources that harvest energy from their environment. Still, the amount of energy achievable by off-the-shelf energy harvesters is very limited, which means that the features and functions of the batteryless devices are heavily restricted. Since waiting for an acknowledgment message after a transmission is energy-costly, especially in the case where no acknowledgment is received and thus re-transmission of the original message is required, existing communication methods for energy-harvesting batteryless devices do not implement any acknowledgment process, but directly perform several retransmissions of the message in order to ensure reliability of the communication. This solution is effective in that it generally allows for a correct reception. However, the solution also has several drawbacks. First of all, in such an implementation where no acknowledgment message is expected, a batteryless device never listens to events occurring in the network it belongs to. Accordingly, in case of configuration changes, for example regarding communication channel, network identifier or address assignment, the batteryless device cannot receive any information, and thus cannot adapt its transmission parameters to the new configuration, rendering further transmissions unsuccessful. Especially the inability to adapt to channel changes is critical, since it will either force the device assigned to receive the communication from the batteryless device to operate on multiple channels, which is technically very challenging due to real-time requirements of several control applications, or force the user to re-commission the batteryless device, which is labour-intensive and thus not acceptable from the user point of view. Secondly, the number of retransmissions is fixed, and does not vary even if one of the first transmissions succeeds. Accordingly, such implementations involve wasting energy for useless transmissions; this energy could be more purposefully used.
Moreover, for energy-saving reasons, all re-transmissions are sent without the proper channel access mechanism CSMA/CA required for correct operation of the network, thus potentially resulting in packet collisions and thus corrupted communication for other devices, batteryless, on the proxy network, or on other surrounding networks using the same frequency band.